A variety of electrical connecting devices are designed for utilization with a flat flexible circuit which may be mounted directly in circuit with terminal pins, for instance. Generally, a flat flexible circuit includes a flat flexible dielectric substrate having one or more holes therein for receiving one or more terminal pins. A ductile conductive film or other circuit trace system is deposited on the substrate in an area at least about the hole or holes. The terminal pins are inserted into the holes in the substrate to establish electrical and mechanical connections between the pins and the flat flexible circuit. Normally, each hole is smaller in diameter than a respective pin. Alternatively, the pin may be punched through the flat flexible circuit to establish the electrical and mechanical connection therewith.
Generally flat terminal blades also have been electrically coupled to flat flexible circuits or substrates. However, because the terminal blades are generally flat, the blades are not inserted into holes in the flat flexible circuit. The blades are coupled to the conductors or conductive film on the circuit substrate by solder or other conductive adhesives.
When using terminal pins, in order to assure good electrical and mechanical connections, solder or other conductive adhesives also are often used. For instance, in U.S. Pat. No. 4,970,624, dated Nov. 13, 1990 and assigned to the assignee of the present invention, uni-axial adhesive is deposited on the flat flexible circuit about the hole which is penetrated by the terminal pin. The adhesive includes a non-conductive base incorporating randomly spaced conductive particles. When the terminal pin is forced through the adhesive, a portion of the adhesive is carried with the terminal pin between the pin and the flat flexible circuit. The carried portion of the adhesive is compressed for establishing contact between the conductive particles and, thereby, conductivity between the terminal pin and the flat flexible circuit, leaving the adhesive other than that portion in a non-conductive state. Such adhesives often are called "Z-axis" adhesives. These adhesives were developed to replace soldering techniques which require specific temperature resistant components and substrates.
Conductive adhesives are used in other applications involving flat flexible circuits. For instance, in U.S. Pat. No. 5,456,616, dated Oct. 10, 1995 and assigned to the assignee of the present invention, the connector housing is fabricated of a die cast metallic material, such as of magnesium, aluminum or the like. The ductile film on the flat flexible circuit is fabricated of a different metallic material, such as copper or the like and, in fact, may be plated with still a different metallic material such as a tin/lead alloy. The conductive film on the flat flexible circuit acts as a ground plane against the rear face of the connector housing. The housing has a plurality of pins which project through holes in the flat flexible circuit. Using a "Z-axis" adhesive between the housing pins and the flat flexible circuit not only is expensive, as described above, but the conductive interface between the different metal components is limited to the areas of pressure. Consequently, that patent teaches the use of an omni-directional conductive adhesive deposited on the conductive film over the areas of the holes therein, the conductive adhesive expanding the conductive interface between the metal housing and the metal ground plane defined by the conductive film.
Although such uses of conductive adhesives, whether the adhesives are Z-axis adhesives or omni-directional adhesives, serve their intended purposes in certain applications, they are relatively expensive both in the cost of the adhesives as well as their methods of use. In addition, the use of either type of conductive adhesive is costly in terms of secondary operations and costs associated with the metal particles, not to mention the problem of clogging adhesive dispensers by the metallic particles.
Because of the problems associated with the use of conductive adhesives, a unique system was devised as disclosed in U.S. Pat. No. 5,384,435, dated Jan. 24, 1995 and assigned to the assignee of the present invention. That patent solves the problems with conductive adhesives by establishing an electrical connection directly between the terminal pin and the flat conductor on the flat flexible substrate by controlling various parameters between the pin and the substrate. In the system of the '435 patent, the terminal pin is round in cross-section, and the round pin is inserted into a round hole in the flat flexible substrate.
Although this system has proven quite effective for electrically coupling terminal pins through holes in flat flexible circuits or substrates, the advantages of such systems would be highly desirable for use with generally flat terminal blades which, as stated above, are soldered or otherwise conductively adhered directly to the conductive film on the circuit substrate. The present invention is directed to satisfying this need and solving the problems of using relatively expensive solder or conductive adhesives to interconnect flat terminals to flat circuits.